Question

Our app has been using this query for a while now:

SELECT id 
FROM invoice 
WHERE id NOT IN 
(SELECT invoice_id FROM invoice_transaction) 

#437 rows returned

In a code review, this query was rewritten with a left outer join:

SELECT invoice.id 
FROM invoice 
LEFT OUTER JOIN invoice_transaction on invoice.id=invoice_transaction.invoice_id 

#586 rows returned

The first query returns 437 rows and the second (supposedly identical) query returns 586 rows. Is this not a valid use of the left outer join?

What would be a better way to rewrite this query?

Thank you!

Answer 1

The following query should return the same results of the first query:

SELECT invoice.id 
FROM invoice 
LEFT OUTER JOIN invoice_transaction 
             on invoice.id = invoice_transaction.invoice_id
WHERE invoice_transaction.invoice_id IS NULL